The disclosure relates generally to additive manufacturing, and more particularly, to a method of selectively modifying an additive manufacturing build strategy parameter for a region of an object.
The pace of change and improvement in the realms of power generation, aviation, and other fields has accompanied extensive research for manufacturing objects used in these fields. Conventional manufacture of objects, such as metallic, plastic or ceramic composite objects, generally includes milling or cutting away regions from a slab of material before treating and modifying the cut material to yield a part, which may have been simulated using computer models, e.g., in drafting software. Manufactured objects which may be formed from metal can include, e.g., airfoil objects for installation in a turbomachine such as an aircraft engine or power generation system.
Additive manufacturing (AM) includes a wide variety of processes of producing an object through the successive layering of material rather than the removal of material. Additive manufacturing can create complex geometries without the use of any sort of tools, molds or fixtures, and with little or no waste material. Instead of machining objects from solid billets of material, much of which is cut away and discarded, the only material used in additive manufacturing is what is required to shape the object.
Additive manufacturing techniques typically include taking a three-dimensional (3D) computer aided design (CAD) object file of the object to be formed, and electronically slicing the object into layers (e.g., 18-102 micrometers thick) to create a file with a two-dimensional image of each layer (including vectors, images or coordinates) that can be used to manufacture the object. The 3D CAD object file can be created in any known fashion, e.g., computer aided design (CAD) system, a 3D scanner, or digital photography and photogrammetry software. The 3D CAD object file may undergo any necessary repair to address errors (e.g., holes, etc.) therein, and may have any CAD format such as a Standard Tessellation Language (STL) file. The 3D CAD object file may then be processed by a preparation software system (sometimes referred to as a “slicer”) that interprets the 3D CAD object file and electronically slices it such that the object can be built by different types of additive manufacturing systems. The preparation software system may be part of the CAD system, part of the computerized AM system or separate from both. The preparation software system may output an object code file in any format capable of being used by the desired computerized AM system. For example, the object code file may be an STL file or an additive manufacturing file (AMF), the latter of which is an international standard that is an extensible markup-language (XML) based format designed to allow any CAD software to describe the shape and composition of any three-dimensional object to be fabricated on any AM printer. Depending on the type of additive manufacturing used, material layers are selectively dispensed, sintered, formed, deposited, etc., to create the object per the object code file.
One form of powder bed infusion (referred to herein as metal powder additive manufacturing) may include direct metal laser melting (DMLM) (also referred to as selective laser melting (SLM)). In metal powder additive manufacturing, metal powder layers are sequentially melted together to form the object. More specifically, fine metal powder layers are sequentially melted after being uniformly distributed using an applicator on a metal powder bed. Each applicator includes an applicator element in the form of a lip, brush, blade or roller made of metal, plastic, ceramic, carbon fibers or rubber that spreads the metal powder evenly over the build platform. The metal powder bed can be moved in a vertical axis. The process takes place in a processing chamber having a precisely controlled atmosphere. Once each layer is created, each two dimensional slice of the object geometry can be fused by selectively melting the metal powder. The melting may be performed by a high powered irradiation beam, such as a 100 Watt ytterbium laser, to fully weld (melt) the metal powder to form a solid metal. The irradiation beam moves in the X-Y direction, and has an intensity sufficient to fully weld (melt) the metal powder to form a solid metal. The metal powder bed may be lowered for each subsequent two dimensional layer, and the process repeats until the object is completely formed.
Some metal powder AM systems employ two or more irradiation devices, e.g., high powered lasers or electron beams, that work together to form an object. Using two or more irradiation devices may be advantageous to create larger objects faster, to allow use of larger build areas or computerized AM systems, and/or improve the accuracy of a build. Typically, for a multiple irradiation device computerized AM system, each two-dimensional image of each layer includes assignments for different irradiation devices to form different regions of the object. The irradiation device assignment can be provided by any of the AM file systems, i.e., the CAD system that creates the original layout of the object, a preparation software system, or the control system of the multiple irradiation device computerized AM system.
One challenge with current AM techniques is that build strategies that direct how an AM system will create a region of an object within each layer are not readily modifiable. For example, for a multiple irradiation device AM system, how two or more irradiation devices will create the region or interact to create the region is not easily modifiable. Build strategy parameters can take a variety of forms. One example build strategy parameter includes the location of a stitching region in an object in which two or more irradiation devices interact to build the object. Stitching regions can have an increased surface roughness or altered material properties that may not be desired to be located in sensitive areas in certain objects, e.g., within a hole that requires precise dimensions or a smooth bearing surface. Conventionally, the location of stitching regions is automatically determined by one of the aforementioned AM file systems. Consequently, prevention of a stitching region being located in a sensitive area within an object cannot be easily controlled. Any changes require labor intensive revision of the object code representative of the object. This challenge exists regardless of the category of additive manufacturing employed.